/* ***************************************************************************
 *
 * ftdriver.h
 *
 * FreeType API for controlling driver modules (specification only).
 *
 * Copyright (C) 2017-2021 by
 * David Turner, Robert Wilhelm, and Werner Lemberg.
 *
 * This file is part of the FreeType project, and may only be used,
 * modified, and distributed under the terms of the FreeType project
 * license, LICENSE.TXT.  By continuing to use, modify, or distribute
 * this file you indicate that you have read the license and
 * understand and accept it fully.
 *
 */


#ifndef FTDRIVER_H_
#define FTDRIVER_H_

#include <freetype/freetype.h>
#include <freetype/ftparams.h>

#ifdef FREETYPE_H
#error "freetype.h of FreeType 1 has been loaded!"
#error "Please fix the directory search order for header files"
#error "so that freetype.h of FreeType 2 is found first."
#endif


FT_BEGIN_HEADER


/* *************************************************************************
 *
 * @section:
 * auto_hinter
 *
 * @title:
 * The auto-hinter
 *
 * @abstract:
 * Controlling the auto-hinting module.
 *
 * @description:
 * While FreeType's auto-hinter doesn't expose API functions by itself,
 * it is possible to control its behaviour with @FT_Property_Set and
 * @FT_Property_Get.  The following lists the available properties
 * together with the necessary macros and structures.
 *
 * Note that the auto-hinter's module name is 'autofitter' for historical
 * reasons.
 *
 * Available properties are @increase-x-height, @no-stem-darkening
 * (experimental), @darkening-parameters (experimental),
 * @glyph-to-script-map (experimental), @fallback-script (experimental),
 * and @default-script (experimental), as documented in the @properties
 * section.
 *
 */


/* *************************************************************************
 *
 * @section:
 * cff_driver
 *
 * @title:
 * The CFF driver
 *
 * @abstract:
 * Controlling the CFF driver module.
 *
 * @description:
 * While FreeType's CFF driver doesn't expose API functions by itself, it
 * is possible to control its behaviour with @FT_Property_Set and
 * @FT_Property_Get.
 *
 * The CFF driver's module name is 'cff'.
 *
 * Available properties are @hinting-engine, @no-stem-darkening,
 * @darkening-parameters, and @random-seed, as documented in the
 * @properties section.
 *
 *
 * **Hinting and anti-aliasing principles of the new engine**
 *
 * The rasterizer is positioning horizontal features (e.g., ascender
 * height & x-height, or crossbars) on the pixel grid and minimizing the
 * amount of anti-aliasing applied to them, while placing vertical
 * features (vertical stems) on the pixel grid without hinting, thus
 * representing the stem position and weight accurately.  Sometimes the
 * vertical stems may be only partially black.  In this context,
 * 'anti-aliasing' means that stems are not positioned exactly on pixel
 * borders, causing a fuzzy appearance.
 *
 * There are two principles behind this approach.
 *
 * 1) No hinting in the horizontal direction: Unlike 'superhinted'
 * TrueType, which changes glyph widths to accommodate regular
 * inter-glyph spacing, Adobe's approach is 'faithful to the design' in
 * representing both the glyph width and the inter-glyph spacing designed
 * for the font.  This makes the screen display as close as it can be to
 * the result one would get with infinite resolution, while preserving
 * what is considered the key characteristics of each glyph.  Note that
 * the distances between unhinted and grid-fitted positions at small
 * sizes are comparable to kerning values and thus would be noticeable
 * (and distracting) while reading if hinting were applied.
 *
 * One of the reasons to not hint horizontally is anti-aliasing for LCD
 * screens: The pixel geometry of modern displays supplies three vertical
 * subpixels as the eye moves horizontally across each visible pixel.  On
 * devices where we can be certain this characteristic is present a
 * rasterizer can take advantage of the subpixels to add increments of
 * weight.  In Western writing systems this turns out to be the more
 * critical direction anyway; the weights and spacing of vertical stems
 * (see above) are central to Armenian, Cyrillic, Greek, and Latin type
 * designs.  Even when the rasterizer uses greyscale anti-aliasing instead
 * of color (a necessary compromise when one doesn't know the screen
 * characteristics), the unhinted vertical features preserve the design's
 * weight and spacing much better than aliased type would.
 *
 * 2) Alignment in the vertical direction: Weights and spacing along the
 * y~axis are less critical; what is much more important is the visual
 * alignment of related features (like cap-height and x-height).  The
 * sense of alignment for these is enhanced by the sharpness of grid-fit
 * edges, while the cruder vertical resolution (full pixels instead of
 * 1/3 pixels) is less of a problem.
 *
 * On the technical side, horizontal alignment zones for ascender,
 * x-height, and other important height values (traditionally called
 * 'blue zones') as defined in the font are positioned independently,
 * each being rounded to the nearest pixel edge, taking care of overshoot
 * suppression at small sizes, stem darkening, and scaling.
 *
 * Hstems (this is, hint values defined in the font to help align
 * horizontal features) that fall within a blue zone are said to be
 * 'captured' and are aligned to that zone.  Uncaptured stems are moved
 * in one of four ways, top edge up or down, bottom edge up or down.
 * Unless there are conflicting hstems, the smallest movement is taken to
 * minimize distortion.
 *
 */


/* *************************************************************************
 *
 * @section:
 * pcf_driver
 *
 * @title:
 * The PCF driver
 *
 * @abstract:
 * Controlling the PCF driver module.
 *
 * @description:
 * While FreeType's PCF driver doesn't expose API functions by itself, it
 * is possible to control its behaviour with @FT_Property_Set and
 * @FT_Property_Get.  Right now, there is a single property
 * @no-long-family-names available if FreeType is compiled with
 * PCF_CONFIG_OPTION_LONG_FAMILY_NAMES.
 *
 * The PCF driver's module name is 'pcf'.
 *
 */


/* *************************************************************************
 *
 * @section:
 * t1_cid_driver
 *
 * @title:
 * The Type 1 and CID drivers
 *
 * @abstract:
 * Controlling the Type~1 and CID driver modules.
 *
 * @description:
 * It is possible to control the behaviour of FreeType's Type~1 and
 * Type~1 CID drivers with @FT_Property_Set and @FT_Property_Get.
 *
 * Behind the scenes, both drivers use the Adobe CFF engine for hinting;
 * however, the used properties must be specified separately.
 *
 * The Type~1 driver's module name is 'type1'; the CID driver's module
 * name is 't1cid'.
 *
 * Available properties are @hinting-engine, @no-stem-darkening,
 * @darkening-parameters, and @random-seed, as documented in the
 * @properties section.
 *
 * Please see the @cff_driver section for more details on the new hinting
 * engine.
 *
 */


/* *************************************************************************
 *
 * @section:
 * tt_driver
 *
 * @title:
 * The TrueType driver
 *
 * @abstract:
 * Controlling the TrueType driver module.
 *
 * @description:
 * While FreeType's TrueType driver doesn't expose API functions by
 * itself, it is possible to control its behaviour with @FT_Property_Set
 * and @FT_Property_Get.  The following lists the available properties
 * together with the necessary macros and structures.
 *
 * The TrueType driver's module name is 'truetype'.
 *
 * A single property @interpreter-version is available, as documented in
 * the @properties section.
 *
 * We start with a list of definitions, kindly provided by Greg
 * Hitchcock.
 *
 * _Bi-Level Rendering_
 *
 * Monochromatic rendering, exclusively used in the early days of
 * TrueType by both Apple and Microsoft.  Microsoft's GDI interface
 * supported hinting of the right-side bearing point, such that the
 * advance width could be non-linear.  Most often this was done to
 * achieve some level of glyph symmetry.  To enable reasonable
 * performance (e.g., not having to run hinting on all glyphs just to get
 * the widths) there was a bit in the head table indicating if the side
 * bearing was hinted, and additional tables, 'hdmx' and 'LTSH', to cache
 * hinting widths across multiple sizes and device aspect ratios.
 *
 * _Font Smoothing_
 *
 * Microsoft's GDI implementation of anti-aliasing.  Not traditional
 * anti-aliasing as the outlines were hinted before the sampling.  The
 * widths matched the bi-level rendering.
 *
 * _ClearType Rendering_
 *
 * Technique that uses physical subpixels to improve rendering on LCD
 * (and other) displays.  Because of the higher resolution, many methods
 * of improving symmetry in glyphs through hinting the right-side bearing
 * were no longer necessary.  This lead to what GDI calls 'natural
 * widths' ClearType, see
 * http://rastertragedy.com/RTRCh4.htm#Sec21.  Since hinting
 * has extra resolution, most non-linearity went away, but it is still
 * possible for hints to change the advance widths in this mode.
 *
 * _ClearType Compatible Widths_
 *
 * One of the earliest challenges with ClearType was allowing the
 * implementation in GDI to be selected without requiring all UI and
 * documents to reflow.  To address this, a compatible method of
 * rendering ClearType was added where the font hints are executed once
 * to determine the width in bi-level rendering, and then re-run in
 * ClearType, with the difference in widths being absorbed in the font
 * hints for ClearType (mostly in the white space of hints); see
 * http://rastertragedy.com/RTRCh4.htm#Sec20.  Somewhat by
 * definition, compatible width ClearType allows for non-linear widths,
 * but only when the bi-level version has non-linear widths.
 *
 * _ClearType Subpixel Positioning_
 *
 * One of the nice benefits of ClearType is the ability to more crisply
 * display fractional widths; unfortunately, the GDI model of integer
 * bitmaps did not support this.  However, the WPF and Direct Write
 * frameworks do support fractional widths.  DWrite calls this 'natural
 * mode', not to be confused with GDI's 'natural widths'.  Subpixel
 * positioning, in the current implementation of Direct Write,
 * unfortunately does not support hinted advance widths, see
 * http://rastertragedy.com/RTRCh4.htm#Sec22.  Note that the
 * TrueType interpreter fully allows the advance width to be adjusted in
 * this mode, just the DWrite client will ignore those changes.
 *
 * _ClearType Backward Compatibility_
 *
 * This is a set of exceptions made in the TrueType interpreter to
 * minimize hinting techniques that were problematic with the extra
 * resolution of ClearType; see
 * http://rastertragedy.com/RTRCh4.htm#Sec1 and
 * https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx.
 * This technique is not to be confused with ClearType compatible widths.
 * ClearType backward compatibility has no direct impact on changing
 * advance widths, but there might be an indirect impact on disabling
 * some deltas.  This could be worked around in backward compatibility
 * mode.
 *
 * _Native ClearType Mode_
 *
 * (Not to be confused with 'natural widths'.)  This mode removes all the
 * exceptions in the TrueType interpreter when running with ClearType.
 * Any issues on widths would still apply, though.
 *
 */


/* *************************************************************************
 *
 * @section:
 * properties
 *
 * @title:
 * Driver properties
 *
 * @abstract:
 * Controlling driver modules.
 *
 * @description:
 * Driver modules can be controlled by setting and unsetting properties,
 * using the functions @FT_Property_Set and @FT_Property_Get.  This
 * section documents the available properties, together with auxiliary
 * macros and structures.
 *
 */


/* *************************************************************************
 *
 * @enum:
 * FT_HINTING_XXX
 *
 * @description:
 * A list of constants used for the @hinting-engine property to select
 * the hinting engine for CFF, Type~1, and CID fonts.
 *
 * @values:
 * FT_HINTING_FREETYPE ::
 * Use the old FreeType hinting engine.
 *
 * FT_HINTING_ADOBE ::
 * Use the hinting engine contributed by Adobe.
 *
 * @since:
 * 2.9
 *
 */
#define FT_HINTING_FREETYPE 0
#define FT_HINTING_ADOBE 1

/* these constants (introduced in 2.4.12) are deprecated */
#define FT_CFF_HINTING_FREETYPE FT_HINTING_FREETYPE
#define FT_CFF_HINTING_ADOBE FT_HINTING_ADOBE


/* *************************************************************************
 *
 * @property:
 * hinting-engine
 *
 * @description:
 * Thanks to Adobe, which contributed a new hinting (and parsing) engine,
 * an application can select between 'freetype' and 'adobe' if compiled
 * with `CFF_CONFIG_OPTION_OLD_ENGINE`.  If this configuration macro
 * isn't defined, 'hinting-engine' does nothing.
 *
 * The same holds for the Type~1 and CID modules if compiled with
 * `T1_CONFIG_OPTION_OLD_ENGINE`.
 *
 * For the 'cff' module, the default engine is 'adobe'.  For both the
 * 'type1' and 't1cid' modules, the default engine is 'adobe', too.
 *
 * @note:
 * This property can be used with @FT_Property_Get also.
 *
 * This property can be set via the `FREETYPE_PROPERTIES` environment
 * variable (using values 'adobe' or 'freetype').
 *
 * @example:
 * The following example code demonstrates how to select Adobe's hinting
 * engine for the 'cff' module (omitting the error handling).
 *
 * ```
 * FT_Library  library;
 * FT_UInt     hinting_engine = FT_HINTING_ADOBE;
 *
 *
 * FT_Init_FreeType( &library );
 *
 * FT_Property_Set( library, "cff",
 * "hinting-engine", &hinting_engine );
 * ```
 *
 * @since:
 * 2.4.12 (for 'cff' module)
 *
 * 2.9 (for 'type1' and 't1cid' modules)
 *
 */


/* *************************************************************************
 *
 * @property:
 * no-stem-darkening
 *
 * @description:
 * All glyphs that pass through the auto-hinter will be emboldened unless
 * this property is set to TRUE.  The same is true for the CFF, Type~1,
 * and CID font modules if the 'Adobe' engine is selected (which is the
 * default).
 *
 * Stem darkening emboldens glyphs at smaller sizes to make them more
 * readable on common low-DPI screens when using linear alpha blending
 * and gamma correction, see @FT_Render_Glyph.  When not using linear
 * alpha blending and gamma correction, glyphs will appear heavy and
 * fuzzy!
 *
 * Gamma correction essentially lightens fonts since shades of grey are
 * shifted to higher pixel values (=~higher brightness) to match the
 * original intention to the reality of our screens.  The side-effect is
 * that glyphs 'thin out'.  Mac OS~X and Adobe's proprietary font
 * rendering library implement a counter-measure: stem darkening at
 * smaller sizes where shades of gray dominate.  By emboldening a glyph
 * slightly in relation to its pixel size, individual pixels get higher
 * coverage of filled-in outlines and are therefore 'blacker'.  This
 * counteracts the 'thinning out' of glyphs, making text remain readable
 * at smaller sizes.
 *
 * For the auto-hinter, stem-darkening is experimental currently and thus
 * switched off by default (this is, `no-stem-darkening` is set to TRUE
 * by default).  Total consistency with the CFF driver is not achieved
 * right now because the emboldening method differs and glyphs must be
 * scaled down on the Y-axis to keep outline points inside their
 * precomputed blue zones.  The smaller the size (especially 9ppem and
 * down), the higher the loss of emboldening versus the CFF driver.
 *
 * Note that stem darkening is never applied if @FT_LOAD_NO_SCALE is set.
 *
 * @note:
 * This property can be used with @FT_Property_Get also.
 *
 * This property can be set via the `FREETYPE_PROPERTIES` environment
 * variable (using values 1 and 0 for 'on' and 'off', respectively).  It
 * can also be set per face using @FT_Face_Properties with
 * @FT_PARAM_TAG_STEM_DARKENING.
 *
 * @example:
 * ```
 * FT_Library  library;
 * FT_Bool     no_stem_darkening = TRUE;
 *
 *
 * FT_Init_FreeType( &library );
 *
 * FT_Property_Set( library, "cff",
 * "no-stem-darkening", &no_stem_darkening );
 * ```
 *
 * @since:
 * 2.4.12 (for 'cff' module)
 *
 * 2.6.2 (for 'autofitter' module)
 *
 * 2.9 (for 'type1' and 't1cid' modules)
 *
 */


/* *************************************************************************
 *
 * @property:
 * darkening-parameters
 *
 * @description:
 * By default, the Adobe hinting engine, as used by the CFF, Type~1, and
 * CID font drivers, darkens stems as follows (if the `no-stem-darkening`
 * property isn't set):
 *
 * ```
 * stem width <= 0.5px:   darkening amount = 0.4px
 * stem width  = 1px:     darkening amount = 0.275px
 * stem width  = 1.667px: darkening amount = 0.275px
 * stem width >= 2.333px: darkening amount = 0px
 * ```
 *
 * and piecewise linear in-between.  At configuration time, these four
 * control points can be set with the macro
 * `CFF_CONFIG_OPTION_DARKENING_PARAMETERS`; the CFF, Type~1, and CID
 * drivers share these values.  At runtime, the control points can be
 * changed using the `darkening-parameters` property (see the example
 * below that demonstrates this for the Type~1 driver).
 *
 * The x~values give the stem width, and the y~values the darkening
 * amount.  The unit is 1000th of pixels.  All coordinate values must be
 * positive; the x~values must be monotonically increasing; the y~values
 * must be monotonically decreasing and smaller than or equal to 500
 * (corresponding to half a pixel); the slope of each linear piece must
 * be shallower than -1 (e.g., -.4).
 *
 * The auto-hinter provides this property, too, as an experimental
 * feature.  See @no-stem-darkening for more.
 *
 * @note:
 * This property can be used with @FT_Property_Get also.
 *
 * This property can be set via the `FREETYPE_PROPERTIES` environment
 * variable, using eight comma-separated integers without spaces.  Here
 * the above example, using `\` to break the line for readability.
 *
 * ```
 * FREETYPE_PROPERTIES=\
 * type1:darkening-parameters=500,300,1000,200,1500,100,2000,0
 * ```
 *
 * @example:
 * ```
 * FT_Library  library;
 * FT_Int      darken_params[8] = {  500, 300,   // x1, y1
 * 1000, 200,   // x2, y2
 * 1500, 100,   // x3, y3
 * 2000,   0 }; // x4, y4
 *
 *
 * FT_Init_FreeType( &library );
 *
 * FT_Property_Set( library, "type1",
 * "darkening-parameters", darken_params );
 * ```
 *
 * @since:
 * 2.5.1 (for 'cff' module)
 *
 * 2.6.2 (for 'autofitter' module)
 *
 * 2.9 (for 'type1' and 't1cid' modules)
 *
 */


/* *************************************************************************
 *
 * @property:
 * random-seed
 *
 * @description:
 * By default, the seed value for the CFF 'random' operator and the
 * similar '0 28 callothersubr pop' command for the Type~1 and CID
 * drivers is set to a random value.  However, mainly for debugging
 * purposes, it is often necessary to use a known value as a seed so that
 * the pseudo-random number sequences generated by 'random' are
 * repeatable.
 *
 * The `random-seed` property does that.  Its argument is a signed 32bit
 * integer; if the value is zero or negative, the seed given by the
 * `intitialRandomSeed` private DICT operator in a CFF file gets used (or
 * a default value if there is no such operator).  If the value is
 * positive, use it instead of `initialRandomSeed`, which is consequently
 * ignored.
 *
 * @note:
 * This property can be set via the `FREETYPE_PROPERTIES` environment
 * variable.  It can also be set per face using @FT_Face_Properties with
 * @FT_PARAM_TAG_RANDOM_SEED.
 *
 * @since:
 * 2.8 (for 'cff' module)
 *
 * 2.9 (for 'type1' and 't1cid' modules)
 *
 */


/* *************************************************************************
 *
 * @property:
 * no-long-family-names
 *
 * @description:
 * If `PCF_CONFIG_OPTION_LONG_FAMILY_NAMES` is active while compiling
 * FreeType, the PCF driver constructs long family names.
 *
 * There are many PCF fonts just called 'Fixed' which look completely
 * different, and which have nothing to do with each other.  When
 * selecting 'Fixed' in KDE or Gnome one gets results that appear rather
 * random, the style changes often if one changes the size and one cannot
 * select some fonts at all.  The improve this situation, the PCF module
 * prepends the foundry name (plus a space) to the family name.  It also
 * checks whether there are 'wide' characters; all put together, family
 * names like 'Sony Fixed' or 'Misc Fixed Wide' are constructed.
 *
 * If `no-long-family-names` is set, this feature gets switched off.
 *
 * @note:
 * This property can be used with @FT_Property_Get also.
 *
 * This property can be set via the `FREETYPE_PROPERTIES` environment
 * variable (using values 1 and 0 for 'on' and 'off', respectively).
 *
 * @example:
 * ```
 * FT_Library  library;
 * FT_Bool     no_long_family_names = TRUE;
 *
 *
 * FT_Init_FreeType( &library );
 *
 * FT_Property_Set( library, "pcf",
 * "no-long-family-names",
 * &no_long_family_names );
 * ```
 *
 * @since:
 * 2.8
 */


/* *************************************************************************
 *
 * @enum:
 * TT_INTERPRETER_VERSION_XXX
 *
 * @description:
 * A list of constants used for the @interpreter-version property to
 * select the hinting engine for Truetype fonts.
 *
 * The numeric value in the constant names represents the version number
 * as returned by the 'GETINFO' bytecode instruction.
 *
 * @values:
 * TT_INTERPRETER_VERSION_35 ::
 * Version~35 corresponds to MS rasterizer v.1.7 as used e.g. in
 * Windows~98; only grayscale and B/W rasterizing is supported.
 *
 * TT_INTERPRETER_VERSION_38 ::
 * Version~38 corresponds to MS rasterizer v.1.9; it is roughly
 * equivalent to the hinting provided by DirectWrite ClearType (as can
 * be found, for example, in the Internet Explorer~9 running on
 * Windows~7).  It is used in FreeType to select the 'Infinality'
 * subpixel hinting code.  The code may be removed in a future version.
 *
 * TT_INTERPRETER_VERSION_40 ::
 * Version~40 corresponds to MS rasterizer v.2.1; it is roughly
 * equivalent to the hinting provided by DirectWrite ClearType (as can
 * be found, for example, in Microsoft's Edge Browser on Windows~10).
 * It is used in FreeType to select the 'minimal' subpixel hinting
 * code, a stripped-down and higher performance version of the
 * 'Infinality' code.
 *
 * @note:
 * This property controls the behaviour of the bytecode interpreter and
 * thus how outlines get hinted.  It does **not** control how glyph get
 * rasterized!  In particular, it does not control subpixel color
 * filtering.
 *
 * If FreeType has not been compiled with the configuration option
 * `TT_CONFIG_OPTION_SUBPIXEL_HINTING`, selecting version~38 or~40 causes
 * an `FT_Err_Unimplemented_Feature` error.
 *
 * Depending on the graphics framework, Microsoft uses different bytecode
 * and rendering engines.  As a consequence, the version numbers returned
 * by a call to the 'GETINFO' bytecode instruction are more convoluted
 * than desired.
 *
 * Here are two tables that try to shed some light on the possible values
 * for the MS rasterizer engine, together with the additional features
 * introduced by it.
 *
 * ```
 * GETINFO framework               version feature
 * -------------------------------------------------------------------
 * 3   GDI (Win 3.1),            v1.0  16-bit, first version
 * TrueImage
 * 33   GDI (Win NT 3.1),         v1.5  32-bit
 * HP Laserjet
 * 34   GDI (Win 95)              v1.6  font smoothing,
 * new SCANTYPE opcode
 * 35   GDI (Win 98/2000)         v1.7  (UN)SCALED_COMPONENT_OFFSET
 * bits in composite glyphs
 * 36   MGDI (Win CE 2)           v1.6+ classic ClearType
 * 37   GDI (XP and later),       v1.8  ClearType
 * GDI+ old (before Vista)
 * 38   GDI+ old (Vista, Win 7),  v1.9  subpixel ClearType,
 * WPF                             Y-direction ClearType,
 * additional error checking
 * 39   DWrite (before Win 8)     v2.0  subpixel ClearType flags
 * in GETINFO opcode,
 * bug fixes
 * 40   GDI+ (after Win 7),       v2.1  Y-direction ClearType flag
 * DWrite (Win 8)                    in GETINFO opcode,
 * Gray ClearType
 * ```
 *
 * The 'version' field gives a rough orientation only, since some
 * applications provided certain features much earlier (as an example,
 * Microsoft Reader used subpixel and Y-direction ClearType already in
 * Windows 2000).  Similarly, updates to a given framework might include
 * improved hinting support.
 *
 * ```
 * version   sampling          rendering        comment
 * x        y       x           y
 * --------------------------------------------------------------
 * v1.0   normal  normal  B/W           B/W    bi-level
 * v1.6   high    high    gray          gray   grayscale
 * v1.8   high    normal  color-filter  B/W    (GDI) ClearType
 * v1.9   high    high    color-filter  gray   Color ClearType
 * v2.1   high    normal  gray          B/W    Gray ClearType
 * v2.1   high    high    gray          gray   Gray ClearType
 * ```
 *
 * Color and Gray ClearType are the two available variants of
 * 'Y-direction ClearType', meaning grayscale rasterization along the
 * Y-direction; the name used in the TrueType specification for this
 * feature is 'symmetric smoothing'.  'Classic ClearType' is the original
 * algorithm used before introducing a modified version in Win~XP.
 * Another name for v1.6's grayscale rendering is 'font smoothing', and
 * 'Color ClearType' is sometimes also called 'DWrite ClearType'.  To
 * differentiate between today's Color ClearType and the earlier
 * ClearType variant with B/W rendering along the vertical axis, the
 * latter is sometimes called 'GDI ClearType'.
 *
 * 'Normal' and 'high' sampling describe the (virtual) resolution to
 * access the rasterized outline after the hinting process.  'Normal'
 * means 1 sample per grid line (i.e., B/W).  In the current Microsoft
 * implementation, 'high' means an extra virtual resolution of 16x16 (or
 * 16x1) grid lines per pixel for bytecode instructions like 'MIRP'.
 * After hinting, these 16 grid lines are mapped to 6x5 (or 6x1) grid
 * lines for color filtering if Color ClearType is activated.
 *
 * Note that 'Gray ClearType' is essentially the same as v1.6's grayscale
 * rendering.  However, the GETINFO instruction handles it differently:
 * v1.6 returns bit~12 (hinting for grayscale), while v2.1 returns
 * bits~13 (hinting for ClearType), 18 (symmetrical smoothing), and~19
 * (Gray ClearType).  Also, this mode respects bits 2 and~3 for the
 * version~1 gasp table exclusively (like Color ClearType), while v1.6
 * only respects the values of version~0 (bits 0 and~1).
 *
 * Keep in mind that the features of the above interpreter versions might
 * not map exactly to FreeType features or behavior because it is a
 * fundamentally different library with different internals.
 *
 */
#define TT_INTERPRETER_VERSION_35 35
#define TT_INTERPRETER_VERSION_38 38
#define TT_INTERPRETER_VERSION_40 40


/* *************************************************************************
 *
 * @property:
 * interpreter-version
 *
 * @description:
 * Currently, three versions are available, two representing the bytecode
 * interpreter with subpixel hinting support (old 'Infinality' code and
 * new stripped-down and higher performance 'minimal' code) and one
 * without, respectively.  The default is subpixel support if
 * `TT_CONFIG_OPTION_SUBPIXEL_HINTING` is defined, and no subpixel
 * support otherwise (since it isn't available then).
 *
 * If subpixel hinting is on, many TrueType bytecode instructions behave
 * differently compared to B/W or grayscale rendering (except if 'native
 * ClearType' is selected by the font).  Microsoft's main idea is to
 * render at a much increased horizontal resolution, then sampling down
 * the created output to subpixel precision.  However, many older fonts
 * are not suited to this and must be specially taken care of by applying
 * (hardcoded) tweaks in Microsoft's interpreter.
 *
 * Details on subpixel hinting and some of the necessary tweaks can be
 * found in Greg Hitchcock's whitepaper at
 * 'https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx'.
 * Note that FreeType currently doesn't really 'subpixel hint' (6x1, 6x2,
 * or 6x5 supersampling) like discussed in the paper.  Depending on the
 * chosen interpreter, it simply ignores instructions on vertical stems
 * to arrive at very similar results.
 *
 * @note:
 * This property can be used with @FT_Property_Get also.
 *
 * This property can be set via the `FREETYPE_PROPERTIES` environment
 * variable (using values '35', '38', or '40').
 *
 * @example:
 * The following example code demonstrates how to deactivate subpixel
 * hinting (omitting the error handling).
 *
 * ```
 * FT_Library  library;
 * FT_Face     face;
 * FT_UInt     interpreter_version = TT_INTERPRETER_VERSION_35;
 *
 *
 * FT_Init_FreeType( &library );
 *
 * FT_Property_Set( library, "truetype",
 * "interpreter-version",
 * &interpreter_version );
 * ```
 *
 * @since:
 * 2.5
 */


/* *************************************************************************
 *
 * @property:
 * glyph-to-script-map
 *
 * @description:
 * **Experimental only**
 *
 * The auto-hinter provides various script modules to hint glyphs.
 * Examples of supported scripts are Latin or CJK.  Before a glyph is
 * auto-hinted, the Unicode character map of the font gets examined, and
 * the script is then determined based on Unicode character ranges, see
 * below.
 *
 * OpenType fonts, however, often provide much more glyphs than character
 * codes (small caps, superscripts, ligatures, swashes, etc.), to be
 * controlled by so-called 'features'.  Handling OpenType features can be
 * quite complicated and thus needs a separate library on top of
 * FreeType.
 *
 * The mapping between glyph indices and scripts (in the auto-hinter
 * sense, see the @FT_AUTOHINTER_SCRIPT_XXX values) is stored as an array
 * with `num_glyphs` elements, as found in the font's @FT_Face structure.
 * The `glyph-to-script-map` property returns a pointer to this array,
 * which can be modified as needed.  Note that the modification should
 * happen before the first glyph gets processed by the auto-hinter so
 * that the global analysis of the font shapes actually uses the modified
 * mapping.
 *
 * @example:
 * The following example code demonstrates how to access it (omitting the
 * error handling).
 *
 * ```
 * FT_Library                library;
 * FT_Face                   face;
 * FT_Prop_GlyphToScriptMap  prop;
 *
 *
 * FT_Init_FreeType( &library );
 * FT_New_Face( library, "foo.ttf", 0, &face );
 *
 * prop.face = face;
 *
 * FT_Property_Get( library, "autofitter",
 * "glyph-to-script-map", &prop );
 *
 * // adjust `prop.map' as needed right here
 *
 * FT_Load_Glyph( face, ..., FT_LOAD_FORCE_AUTOHINT );
 * ```
 *
 * @since:
 * 2.4.11
 *
 */


/* *************************************************************************
 *
 * @enum:
 * FT_AUTOHINTER_SCRIPT_XXX
 *
 * @description:
 * **Experimental only**
 *
 * A list of constants used for the @glyph-to-script-map property to
 * specify the script submodule the auto-hinter should use for hinting a
 * particular glyph.
 *
 * @values:
 * FT_AUTOHINTER_SCRIPT_NONE ::
 * Don't auto-hint this glyph.
 *
 * FT_AUTOHINTER_SCRIPT_LATIN ::
 * Apply the latin auto-hinter.  For the auto-hinter, 'latin' is a very
 * broad term, including Cyrillic and Greek also since characters from
 * those scripts share the same design constraints.
 *
 * By default, characters from the following Unicode ranges are
 * assigned to this submodule.
 *
 * ```
 * U+0020 - U+007F  // Basic Latin (no control characters)
 * U+00A0 - U+00FF  // Latin-1 Supplement (no control characters)
 * U+0100 - U+017F  // Latin Extended-A
 * U+0180 - U+024F  // Latin Extended-B
 * U+0250 - U+02AF  // IPA Extensions
 * U+02B0 - U+02FF  // Spacing Modifier Letters
 * U+0300 - U+036F  // Combining Diacritical Marks
 * U+0370 - U+03FF  // Greek and Coptic
 * U+0400 - U+04FF  // Cyrillic
 * U+0500 - U+052F  // Cyrillic Supplement
 * U+1D00 - U+1D7F  // Phonetic Extensions
 * U+1D80 - U+1DBF  // Phonetic Extensions Supplement
 * U+1DC0 - U+1DFF  // Combining Diacritical Marks Supplement
 * U+1E00 - U+1EFF  // Latin Extended Additional
 * U+1F00 - U+1FFF  // Greek Extended
 * U+2000 - U+206F  // General Punctuation
 * U+2070 - U+209F  // Superscripts and Subscripts
 * U+20A0 - U+20CF  // Currency Symbols
 * U+2150 - U+218F  // Number Forms
 * U+2460 - U+24FF  // Enclosed Alphanumerics
 * U+2C60 - U+2C7F  // Latin Extended-C
 * U+2DE0 - U+2DFF  // Cyrillic Extended-A
 * U+2E00 - U+2E7F  // Supplemental Punctuation
 * U+A640 - U+A69F  // Cyrillic Extended-B
 * U+A720 - U+A7FF  // Latin Extended-D
 * U+FB00 - U+FB06  // Alphab. Present. Forms (Latin Ligatures)
 * U+1D400 - U+1D7FF // Mathematical Alphanumeric Symbols
 * U+1F100 - U+1F1FF // Enclosed Alphanumeric Supplement
 * ```
 *
 * FT_AUTOHINTER_SCRIPT_CJK ::
 * Apply the CJK auto-hinter, covering Chinese, Japanese, Korean, old
 * Vietnamese, and some other scripts.
 *
 * By default, characters from the following Unicode ranges are
 * assigned to this submodule.
 *
 * ```
 * U+1100 - U+11FF  // Hangul Jamo
 * U+2E80 - U+2EFF  // CJK Radicals Supplement
 * U+2F00 - U+2FDF  // Kangxi Radicals
 * U+2FF0 - U+2FFF  // Ideographic Description Characters
 * U+3000 - U+303F  // CJK Symbols and Punctuation
 * U+3040 - U+309F  // Hiragana
 * U+30A0 - U+30FF  // Katakana
 * U+3100 - U+312F  // Bopomofo
 * U+3130 - U+318F  // Hangul Compatibility Jamo
 * U+3190 - U+319F  // Kanbun
 * U+31A0 - U+31BF  // Bopomofo Extended
 * U+31C0 - U+31EF  // CJK Strokes
 * U+31F0 - U+31FF  // Katakana Phonetic Extensions
 * U+3200 - U+32FF  // Enclosed CJK Letters and Months
 * U+3300 - U+33FF  // CJK Compatibility
 * U+3400 - U+4DBF  // CJK Unified Ideographs Extension A
 * U+4DC0 - U+4DFF  // Yijing Hexagram Symbols
 * U+4E00 - U+9FFF  // CJK Unified Ideographs
 * U+A960 - U+A97F  // Hangul Jamo Extended-A
 * U+AC00 - U+D7AF  // Hangul Syllables
 * U+D7B0 - U+D7FF  // Hangul Jamo Extended-B
 * U+F900 - U+FAFF  // CJK Compatibility Ideographs
 * U+FE10 - U+FE1F  // Vertical forms
 * U+FE30 - U+FE4F  // CJK Compatibility Forms
 * U+FF00 - U+FFEF  // Halfwidth and Fullwidth Forms
 * U+1B000 - U+1B0FF // Kana Supplement
 * U+1D300 - U+1D35F // Tai Xuan Hing Symbols
 * U+1F200 - U+1F2FF // Enclosed Ideographic Supplement
 * U+20000 - U+2A6DF // CJK Unified Ideographs Extension B
 * U+2A700 - U+2B73F // CJK Unified Ideographs Extension C
 * U+2B740 - U+2B81F // CJK Unified Ideographs Extension D
 * U+2F800 - U+2FA1F // CJK Compatibility Ideographs Supplement
 * ```
 *
 * FT_AUTOHINTER_SCRIPT_INDIC ::
 * Apply the indic auto-hinter, covering all major scripts from the
 * Indian sub-continent and some other related scripts like Thai, Lao,
 * or Tibetan.
 *
 * By default, characters from the following Unicode ranges are
 * assigned to this submodule.
 *
 * ```
 * U+0900 - U+0DFF  // Indic Range
 * U+0F00 - U+0FFF  // Tibetan
 * U+1900 - U+194F  // Limbu
 * U+1B80 - U+1BBF  // Sundanese
 * U+A800 - U+A82F  // Syloti Nagri
 * U+ABC0 - U+ABFF  // Meetei Mayek
 * U+11800 - U+118DF // Sharada
 * ```
 *
 * Note that currently Indic support is rudimentary only, missing blue
 * zone support.
 *
 * @since:
 * 2.4.11
 *
 */
#define FT_AUTOHINTER_SCRIPT_NONE 0
#define FT_AUTOHINTER_SCRIPT_LATIN 1
#define FT_AUTOHINTER_SCRIPT_CJK 2
#define FT_AUTOHINTER_SCRIPT_INDIC 3


/* *************************************************************************
 *
 * @struct:
 * FT_Prop_GlyphToScriptMap
 *
 * @description:
 * **Experimental only**
 *
 * The data exchange structure for the @glyph-to-script-map property.
 *
 * @since:
 * 2.4.11
 *
 */
typedef struct FT_Prop_GlyphToScriptMap_ {
    FT_Face face;
    FT_UShort *map;
} FT_Prop_GlyphToScriptMap;


/* *************************************************************************
 *
 * @property:
 * fallback-script
 *
 * @description:
 * **Experimental only**
 *
 * If no auto-hinter script module can be assigned to a glyph, a fallback
 * script gets assigned to it (see also the @glyph-to-script-map
 * property).  By default, this is @FT_AUTOHINTER_SCRIPT_CJK.  Using the
 * `fallback-script` property, this fallback value can be changed.
 *
 * @note:
 * This property can be used with @FT_Property_Get also.
 *
 * It's important to use the right timing for changing this value: The
 * creation of the glyph-to-script map that eventually uses the fallback
 * script value gets triggered either by setting or reading a
 * face-specific property like @glyph-to-script-map, or by auto-hinting
 * any glyph from that face.  In particular, if you have already created
 * an @FT_Face structure but not loaded any glyph (using the
 * auto-hinter), a change of the fallback script will affect this face.
 *
 * @example:
 * ```
 * FT_Library  library;
 * FT_UInt     fallback_script = FT_AUTOHINTER_SCRIPT_NONE;
 *
 *
 * FT_Init_FreeType( &library );
 *
 * FT_Property_Set( library, "autofitter",
 * "fallback-script", &fallback_script );
 * ```
 *
 * @since:
 * 2.4.11
 *
 */


/* *************************************************************************
 *
 * @property:
 * default-script
 *
 * @description:
 * **Experimental only**
 *
 * If FreeType gets compiled with `FT_CONFIG_OPTION_USE_HARFBUZZ` to make
 * the HarfBuzz library access OpenType features for getting better glyph
 * coverages, this property sets the (auto-fitter) script to be used for
 * the default (OpenType) script data of a font's GSUB table.  Features
 * for the default script are intended for all scripts not explicitly
 * handled in GSUB; an example is a 'dlig' feature, containing the
 * combination of the characters 'T', 'E', and 'L' to form a 'TEL'
 * ligature.
 *
 * By default, this is @FT_AUTOHINTER_SCRIPT_LATIN.  Using the
 * `default-script` property, this default value can be changed.
 *
 * @note:
 * This property can be used with @FT_Property_Get also.
 *
 * It's important to use the right timing for changing this value: The
 * creation of the glyph-to-script map that eventually uses the default
 * script value gets triggered either by setting or reading a
 * face-specific property like @glyph-to-script-map, or by auto-hinting
 * any glyph from that face.  In particular, if you have already created
 * an @FT_Face structure but not loaded any glyph (using the
 * auto-hinter), a change of the default script will affect this face.
 *
 * @example:
 * ```
 * FT_Library  library;
 * FT_UInt     default_script = FT_AUTOHINTER_SCRIPT_NONE;
 *
 *
 * FT_Init_FreeType( &library );
 *
 * FT_Property_Set( library, "autofitter",
 * "default-script", &default_script );
 * ```
 *
 * @since:
 * 2.5.3
 *
 */


/* *************************************************************************
 *
 * @property:
 * increase-x-height
 *
 * @description:
 * For ppem values in the range 6~<= ppem <= `increase-x-height`, round
 * up the font's x~height much more often than normally.  If the value is
 * set to~0, which is the default, this feature is switched off.  Use
 * this property to improve the legibility of small font sizes if
 * necessary.
 *
 * @note:
 * This property can be used with @FT_Property_Get also.
 *
 * Set this value right after calling @FT_Set_Char_Size, but before
 * loading any glyph (using the auto-hinter).
 *
 * @example:
 * ```
 * FT_Library               library;
 * FT_Face                  face;
 * FT_Prop_IncreaseXHeight  prop;
 *
 *
 * FT_Init_FreeType( &library );
 * FT_New_Face( library, "foo.ttf", 0, &face );
 * FT_Set_Char_Size( face, 10 * 64, 0, 72, 0 );
 *
 * prop.face  = face;
 * prop.limit = 14;
 *
 * FT_Property_Set( library, "autofitter",
 * "increase-x-height", &prop );
 * ```
 *
 * @since:
 * 2.4.11
 *
 */


/* *************************************************************************
 *
 * @struct:
 * FT_Prop_IncreaseXHeight
 *
 * @description:
 * The data exchange structure for the @increase-x-height property.
 *
 */
typedef struct FT_Prop_IncreaseXHeight_ {
    FT_Face face;
    FT_UInt limit;
} FT_Prop_IncreaseXHeight;


/* *************************************************************************
 *
 * @property:
 * warping
 *
 * @description:
 * **Obsolete**
 *
 * This property was always experimental and probably never worked
 * correctly.  It was entirely removed from the FreeType~2 sources.  This
 * entry is only here for historical reference.
 *
 * Warping only worked in 'normal' auto-hinting mode replacing it.  The
 * idea of the code was to slightly scale and shift a glyph along the
 * non-hinted dimension (which is usually the horizontal axis) so that as
 * much of its segments were aligned (more or less) to the grid.  To find
 * out a glyph's optimal scaling and shifting value, various parameter
 * combinations were tried and scored.
 *
 * @since:
 * 2.6
 *
 */


/* */


FT_END_HEADER


#endif /* FTDRIVER_H_ */


/* END */
